The present invention relates to a dielectric ceramic composition of ferro-electric nature, with a barium titanate basis, as well as a capacitor using such a composition. It also relates to a process for manufacturing this composition.
Barium titanate based ceramic compositions are well known particularly in their applications for forming capacitors. They have in fact a very high dielectric constant making them quite well adapted to such a use. Such ceramic compositions, well-known to a man skilled in the art under the term "type II", are described for example in U.S. Pat. Nos. 2,402,518, 2,443,211 and 3,529,978.
Generally, the ceramic compositions are sintered in air or in a reducing atmosphere at temperatures close to 1200.degree. to 1400.degree. C. When capacitors are formed, such for example as capacitors of the multi-layer type, the metal electrodes of these capacitors are of course deposited on the ceramic material before sintering. Consequently, this requires using electrodes made from precious metals such as platinum, palladium, gold or alloys thereof. These electrodes are generally deposited by silk screen printing.
Such ceramic compositions in their use for manufacturing capacitors present then essentially two drawbacks:
precious metals are required for forming the electrodes, which increases considerably the cost of such capacitors, PA1 the high sintering temperature increases the risks of interaction between the ceramic and the electrodes, which correspondingly increases the probability of defects in said electrodes.
So, attempts have been made recently to perfect dielectric ceramic compositions allowing common metal to be used, of a much lower price, while lowering the sintering temperature of said compositions.